Affiliated project

Dissipationless transport in two dimensions: the electronic Kagome lattice

We aim to realize dissipationless electronic transport in an electronic kagome lattice, i.e. a two-dimensional (2D) network of corner-sharing triangles, by stacking a twisted germanene layer on-top of another germanene layer. Germanene, the germanium analogue of graphene, shares many properties with graphene. Both 2D materials have a honeycomb structure and host Dirac fermions. There is, however, also a very important difference between these two materials, which plays a crucial role in this proposal. The graphene lattice is fully planar, whereas the germanene lattice is buckled, i.e. the two triangular sub-lattices, labelled A and B, are slightly displaced with respect to each other in a direction normal to the layer. This buckling is a unique feature that offers the possibility to realize an electronic kagome lattice.

Owing to this buckling, AA, BB, AB and BA stacked atom configurations occur in four flavors: up-up, down-up, down-up and down-down, respectively. Since these four flavors have different atom-to-atom separations and thus also different interlayer interaction (hopping) energies the moiré lattice is electronically modulated, resulting in an electronic kagome lattice.

A twisted bilayer germanene exhibits a moiré pattern consisting of AB and BA stacked domains separated by domain walls. We will apply a transverse electric field in order to break the inversion symmetry of these AB and BA domains. The AB and BA domains have opposite valley Chern numbers and therefore a 2D kagome network of one-dimensional (1D) conducting channels that are protected by no-valley symmetry will emerge at the AB/BA domain boundaries upon the application of an electric field (in 0.6o twisted bilayer graphene we already demonstrated the existence of a 2D triangular network of topologically protected 1D conducting channels).

The electronic and transport properties of this 2D kagome network of topologically protected 1D channels will be studied with variable temperature (4-) tip scanning tunnelling microscopy (STM) and spectroscopy (STS). The robustness against backscattering in these 1D channels allows for dissipationless 2D electronic transport in the twisted bilayer germanene and opens the door to novel electronic field-effect based device applications, such as a twisted bilayer germanene transistor.

This project is funded by a NWO-M grant